pkg/runtime/sys_darwin_amd64.s: fixes syscall select nr
pkg/runtime/sys_linux_arm.s: uses newselect instead of the now unimplemented
        (old) select, also fixes the wrong div/mod statements in runtime.usleep.
Fixes #2633

R=golang-dev, dave, rsc
CC=golang-dev
https://golang.org/cl/5504096